The heat wave that has gripped California for a week took a dramatic turn Thursday as lightning storms sparked brush fires, knocked out power to thousands and caused downpours across the region.

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Lightning strikes were reported in many areas Thursday, with some sparking a series of brush fires near the 5 Freeway in the Santa Clarita Valley.

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Meanwhile, the record heat continued to tax the power grid.

Los Angeles Department of Water and Power customers used more electricity on Thursday battling the heat wave than has ever been used in the agency’s history, DWP officials announced. Customers hit a peak demand of 6,502 megawatts at 4:15 p.m., shattering the previous record of 6,396 megawatts on Sept. 16, 2014. The agency expects a new record to be set Friday as the heat wave continues.

The California Independent System Operator called for voluntary electricity conservation on Friday.

In Boyle Heights, an estimated 11,000 residents were without power overnight Wednesday as high demand overloaded equipment to the point of failure. Power was restored by 6 a.m. Thursday, officials said.

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The heat wave is part of a larger high-pressure system that has settled over the Great Basin and has been broiling states from California to Utah and Arizona to New Mexico.

The weather pattern is also at least partially responsible for the behavior of Hurricane Harvey in Texas, said Bill Patzert, a climatologist with NASA’s Jet Propulsion Laboratory. The system acted as a barrier that blocked Harvey’s path inland. The storm was stopped in its tracks right over Houston, where it continued sucking up moisture from the Gulf of Mexico and raining it down on the flooded landscape below.